THE EARTHQUAKE ADVANCE THEORY 191
its cause, in those remote regions where the conditions are favorable, but which are as yet little studied, is so slight that, even though advance occurs, it may be undetected.
Other Advancing Glaciers. With the discovery of a new cause for the advance of glaciers, which cannot have been considered in the explanations of glacier advances observed prior to this, we naturally consider the question whether the new theory will not explain some of the old advances. We have not found time to make an exhaustive study of the literature of advancing glaciers outside of Alaska to see whether there are indications that this new theory will apply to any of the old cases. We have been deterred from undertaking it partly because of the desire to have the theory discussed and further observations made first, and partly because there seems at least an even chance that such a study of the literature would end only in inconclusive results, since critical observations may not be recorded. It is, for example, possible that the reported great advance of some of the Himalayan glaciers, and the notable advance and transformation of SefstriJm Glacier in Spitzbergen between 1882 and 1896, and of the neighboring Wahlenberg Glacier between 1896 and 1908, while other neighboring glaciers were receding, may be a response to the influence of earthquake shaking of an undetermined period.
There are two points of a general nature bearing on this subject which we wish to make before considering the possible extension of the earthquake theory to other advancing glaciers of Alaska. One of these is the proposition that in small glaciers with broad reservoirs, like the Vernagt Glacier in the Tyrol, the phenomena of advance as the result of the fall of unusual numbers of avalanches without earthquake shaking would imitate those of the advance of larger glaciers under the impulse of more avalanching under vigorous earthquake shaking. Two cases of the latter sort are the little Boveyre Glacier in Valais, Switzerland, which advanced because of great increase of material due to an avalanche, and the Stutfield Glacier of Canada which advanced about half a mile and destroyed a fringing forest, when covered with d£bris by great avalanches.
The second proposition is that in larger glaciers moderate avalanching under the influence of moderate earthquake shaking would result in a response of far less vigor and extent than that observed in the Yakutat Bay glaciers. If this proposition is correct, it is reasonable to expect that some advances of moderate amount, and even without accompanying breaking of the surface, may follow earthquake shaking in the snowfleld region. It is well established that there are moderate fluctuations of glacier fronts in the Alps, and elsewhere, as a result of climatic variations; but there are also exceptional changes in position of the ice fronts. The application of the avalanche theory, either as a result of earthquake shaking or of other cause, to some such variations in glaciers is possible. It will be interesting to see the theory put to a test in some such case.
In Alaska, outside the Yakutat Bay region, there have been many changes in the position of glacier fronts within the period of observation, and some of these may be due to the effects of earthquake shaking. Unfortunately observations on most of these glaciers are of too limited a nature, and for too short a tune, and our knowledge of the extent and nature of preceding earthquake shocks, and of the amount and variation of the snowfall of the Alaskan coastal region, is too slight to permit us to enter into a full or conclusive discussion of the possible cause for these variations. Yet there are some notable facts leading to tentative conclusions, which may be stated.
In 1892 Russell wrote his paper on Climatic Changes Indicated by the Glaciers of